1. Field of the Invention
The subject invention relates to corrosion inhibitors prepared by reacting certain imidazolines or precursors thereof with sulfur. The corrosion inhibitors are particularly useful in inhibiting the corrosion of metal tanks caused by CO.sub.2 and H.sub.2 S ("acid gas") during the transport and storage of crude oils.
2. Description of the Prior Art
It is known to inject a solution or dispersion of corrosion inhibitors into crude oil during oil recovery and during the transport or storage of oil so that a protective layer forms on the surfaces of the metal parts coming into contact with the oil. The crude oil emulsions usually contain saltwater and in many cases, depending upon the origin of the oil, H.sub.2 S and CO.sub.2 which have a pronounced corrosive effect. The corrosion inhibitors to be used for this purpose should be soluble in oil and should at least be dispersible in saltwater so that they can have an optimum effect.
German Published Application No. 2,846,979 describes corrosion inhibitors for this purpose which consist of an imidazoline salt, an oil-soluble solvent for the imidazoline salt, and a hydrocarbon oil. The problem with these inhibitors, however, is that the imidazoline salts described in the referenced literature do not sufficiently suppress the corrosion caused by H.sub.2 S and CO.sub.2, which are often present in the crude oil which is essentially a water-in-oil emulsion, particularly a saltwater-in-oil emulsion. In addition to this, the use of imidazolines under these circumstances is complicated because they must be used together with specific solvents. Moreover, the costs of the hydrocarbon oil is high.
U.S. Pat. No. 3,062,612 describes a process for preventing the corrosion of iron from acid corrosion whereby a finely distributed sulfur together with, among other things, long chained fatty acids, aliphatic amines and/or quaternary ammonium salts of these amines, imidazolines, or organic sulfides are added to the corroding medium. However, this patent relates to a different problem than the subject invention, (it is concerned with corrosion protection agents used for aqueous acid solutions and not for water-in-oil emulsions where the question of solubility is of significant importance) and only ethoxystearylimidazoline is mentioned by way of example in addition to other amines. The imidazoline precursors which are used in accordance with the subject invention to prepare the corrosion inhibitors are not described anywhere in this patent. Furthermore, it has been shown that a mixture of elementary sulfur and ethoxystearylimidazoline brings about totally unsatisfactory results with respect to corrosion protection when used according to this invention in an H.sub.2 S containing saltwater-in-oil emulsion.